This invention relates to a screw-actuated load clamp for mounting on a materials handling machine and, more particularly, to a carton clamp specially adapted for use on an automatically-guided vehicle.
Due to the advent of the microprocessor, warehouses and loading docks have become automated such that materials handling vehicles employing load clamps may be programmed to retrieve or stack loads automatically. Without a human operator, however, the mechanical actuation of the clamp arms must be extremely accurate. That is, without the intervention of a human to compensate for any mispositioning of the clamp arms, the interaction of the electronic control system and the mechanical clamp arm actuators must provide clamp arm positioning within very close tolerance limits.
In addition to the requirement for highly accurate control of the clamp arms, the mechanical clamp arm actuators must also provide sufficient clamping force to support, by frictional gripping, loads which may weigh on the order of several thousand pounds. Hydraulic rams have normally been relied upon in the past to supply such clamping force in load clamps controlled by a human operator. In some of these hydraulically-actuated clamps, such as those exemplified by Rodman U.S. Pat. No. 2,726,780 and Quayle U.S. Pat. No. 3,166,207, each hydraulic ram is attached at one of its ends to a respective clamp arm, the other end being fixed to the clamp frame upon which the clamp arms are movably mounted. In such arrangement, if each ram produces the same predetermined force, two such rams are needed to produce a clamping force between the two arms equal to such predetermined force. In other arrangements, each end of a single hydraulic ram has been connected to a respective arm as exemplified by Jewell et al. U.S. Pat. No. 2,706,570, Arnot U.S. Pat. No. 2,911,793 and Roose U.S. Pat. No. 4,049,140. In the latter arrangements, only a single hydraulic ram producing a predetermined force is necessary to produce the same clamping force between the two clamp arms, thereby effectively doubling the clamping force provided by each ram. However, a drawback of the latter arrangements, which dispense with any fixed coupling between the ram and the clamp frame, is that the ram and clamp arms thereby become freely movable with respect to the frame producing what will hereinafter be referred to as a "free-floating" configuration. Such free-floating configurations are incapable of controlling clamp arm position.
Although hydraulic rams in either one of the above-described two arrangements have normally been relied upon in the past to supply clamping force in load clamps controlled by a human operator, such rams are not well adapted for clamp arm actuation when used with automatically-guided vehicles because of the expense and difficulty of interfacing them with a microprocessor so as to achieve the high degree of accuracy needed for automatic operation. Moreover, in some cases, the absence of a convenient source of pressurized fluid dictates against the use of hydraulic rams in clamps for automatically guided vehicles.
In the past there have been available electric motor-driven screw-type linear actuators, which can provide a high degree of accuracy for positioning mechanical elements, which do not require a source of pressurized hydraulic fluid, and which can be easily interfaced with microprocessor-based electrical controls. However, with a few exceptions such as those shown in Smart U.S. Pat. No. 4,381,166 and Puckett U.S. Pat. No. 2,846,018, screw-type linear actuators have not been favored over hydraulic actuators in vehicular load-handling devices. When they are used, it is normally not for the purpose of providing a clamping force but merely to position mechanical elements. This is because screw-type linear actuators are generally capable of producing far less force in relation to their size than are hydraulic ram assemblies. A free-floating screw-type actuator would at least tend to double the clamping force obtainable from the actuator for the reasons described previously, but this would introduce the problems of how compatibly to make the actuator both free-floating and motor-actuated, and of how to provide precise position control of the screw-actuated arms compatibly with the free-floating arrangement.
Accordingly, what is needed is a load clamp specially adapted for use on automatically-guided vehicles by its utilization of motor-powered screw-type clamping actuators capable of compatibly providing both high clamping force and a high degree of positioning accuracy of the clamp arms.